The drug marijuana is derived from the leaves, stems and other parts of the hemp plant Cannabis sativa, contains delta-9-tetrahydrocannabinol, or THC, a psychoactive chemical which affects areas of the brain associated with pleasure, memory, thinking and coordinated movement. Although Federal law prohibits marijuana possession, distribution or use, 18 states and the District of Columbia now permit marijuana use for medicinal purposes and Colorado and Washington permit recreational use of marijuana among adults.Quest Diagnostics is a leader in prescription and workplace drug monitoring by diagnostic testing. The company's Drug Testing Index™ is widely considered a benchmark in national trends of drug use by American workers. The company extended its drug monitoring services with the addition of a new portfolio of prescription drug monitoring services for clinicians in 2010. A separate press release issued last week by Quest Diagnostics provides additional information on the report's findings on overall prescription drug misuse rates. Study Strengths and LimitationsThe study's strengths are its size and national scope; use of an objective laboratory method, versus surveys or polls, which may be subject to user misrepresentation or error; confirmation of all positive drug screens by mass spectrometry, the most advanced drug testing method; and inclusion of patients under care by clinicians in a primary care or pain-management setting, but exclusion of those in drug rehabilitation or addiction treatment settings, where unusually high rates of drug misuse may be expected. Study limitations include geographic disparities; inability to confirm drug misuse through access to medical records or clinical evaluation; and technological factors and patient variations, such as drug metabolism and hydration state, that may affect the reliability of a minority of results. Quest Diagnostics does not provide services to all clinicians in the U.S., so results are not broadly representative of all patients taking prescription medications in the U.S. It is also possible some clinicians tested patients due to appropriate suspicions of drug misuse, and that some clinicians omitted to specify all drugs prescribed for the patient on a test order, skewing some results.